Synthetic oligonucleotides of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) whose base sequences are known have become extremely useful and important through the development of molecular biology and of genetic engineering in particular. These synthetic oligonucleotides have been widely used in the isolation and synthesis of structural genes, DNA sequencing, site-specific mutagenesis and medical research.
It is well known that oligonucleotide synthesis proceeds more easily, efficiently and less expensively when the oligonucleotides are assembled on a solid support. A solid support plays a unique and crucial role in solid-phase synthesis. A kinetic study of condensation reactions indicates that the condensations follow pseudo first-order kinetics. The rate constant decreases as the coupling units increase from monomers to dimers to trimers. S. Ikuta, R. Chattopadhyaya and R. E. Dickerson, Nucl. Acids Res., 12, 6511-6522 (1984). Steric hindrance and surface repulsion encountered during nucleoside addition apparently increases with larger building blocks.
In spite of many efforts studying polymer support DNA synthesis, most practical assemblies of oligonucleotides have been limited to 30-40 bases. One of the exceptions is phosphoramidite DNA synthesis on a long chain alkylamine (LCAA) controlled pore glass (CPG) solid support. S. P. Adams, K. S. Kavka, E. J. Wykes, S. B. Holder and G. R. Galluppi, J. Am. Chem. Soc., 105, 661-663 (1983); G. R. Gough, M. J. Bruden and P. T. Gilham, Tetrahedron Letters, 4177-4180 (1981). The superiority of this support appears to be due to the introduction of a "long chain" spacer between the polymer support and the first nucleoside, in that the undesired steric hindrance and repulsion may be significantly reduced. In fact, aminopropylated CPG, which provides only a "short" spacer arm is a much less desired support as less effective nucleotide couplings were found when it was used. H. Koster, J. Berimat, J. McManus, A. Walter, A. Strimpe, Ch. K. Narang and N. D. Sinba, Tetrahedron Letters, 40, 103-112 (1984). Unfortunately, however, LCAA-CPG must be prepared through a multistep, labor intensive process. It is desired, therefore, to produce a relatively inexpensive, readily-available, easily prepared synthesis support which contains all of the advantages of the previously mentioned support.